C1orf27 controls the ER‐to‐Golgi traffic of GPCRs via direct interaction

C1orf27 is a human homolog of odorant response abnormal 4 which was originally identified as an endoplasmic reticulum (ER) membrane protein to regulate the delivery of odorant G‐protein‐coupled receptors (GPCRs) to cilia in C. elegans chemosensory neurons. However, its functions in the trafficking of mammalian GPCRs remain poorly understood. Here, we used α 2 ‐adrenergic receptors (ARs) as models to define the role of C1orf27 in the biosynthesis and anterograde trafficking of GPCRs and elucidate the underlying mechanisms in several mammalian cells. We found that siRNA‐mediated depletion of C1orf27 significantly reduced the cell surface expression of α 2A ‐ and α 2B ‐ARs and in parallel receptor‐mediated signaling as measured by MAPK activation. Confocal microscopy revealed that the receptors were restricted in the perinuclear region and extensively co‐localized with the ER marker calregulin in C1orf27 siRNA‐treated cells. In contrast, C1orf27 knockdown did not affect the ER‐Golgi‐cell surface transport of non‐GPCR plasma membrane proteins, such as vesicular stomatitis virus glycoprotein. We also found that C1orf27 directly interacted with both receptors and the interactions were ionic in nature. Interestingly, two C1orf27‐binding sites were identified in the third intracellular loop (ICL3) and the C‐terminus of α 2A ‐AR, whereas only one binding domain was found in the ICL3 of α 2B ‐AR. Furthermore, the deletion of C1orf27‐binding domains clearly impaired the cell surface transport of the receptors, suggesting an important role of the interaction in receptor forward trafficking. Altogether these data have demonstrated that C1orf27 selectively modulates the ER‐to‐Golgi traffic of GPCRs which is likely mediated through direct interaction. Support or Funding Information NIH R01 GM119815